Photographic reproduction process using photopolymerizable resins and new images obtained



United States Patent C) 3,236,647 PHOTOGRAPHIC REPRGDUCTHON PRQCESS USING PHGTUPGLYMERHZABLE RESKNS AND NEW IMAGES UBTAINED Georges A. Phlipot, Paris, France, assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Dec. 26, 1961, $er. No. 162,257 Claims priority, application France, Jan. 5, 1961, 848,867 Claims. (Cl. 96-34) This invention relates to a new process for photographic reproduction on various supports and, in particular, on paper, film, glass and ceramic material, wherein dimerizable light-setting resins are used and which permits the reproduction of continuous tone images. The invention also relates to the resulting products bearing particularly stable images.

Synthetic light-setting polymers have generally been used for copying line or half-tone images in the form of resists. Thus, polyvinyl cinnamate and polyesters of diols and cinnamylidene malonic acid have been used in the preparation of etched electric circuits, in process work and in lithographic printing processes. Many other lightsensitive resins capable of being used for such purposes have also been prepared. Such processes resort to the property of these polymers of becoming insoluble in certain solvents when they are exposed to light, the latent image formed by the photographic exposure of a coating of such polymers being developed by dissolving and removing the unexposed areas. The resulting resist may then be dyed or inked in order to obtain a more visible image. For obtaining pigmented images with such polymers, it has been proposed to incorporate pigments to the light-sensitive resin coating prior to light exposure. Although it permits to obtain interesting results, this process shows several disadvantages. It requires carrying out the so-called wash-ofi? operation which consists of dissolving out the unexposed areas as in the aforementioned processes. This wash-ofi operation, which necessitates the handling of rather important quantities of solvents, sometimes renders critical the .adhesiveness of the coating on the support, particularly when the latter has a very smooth surface. Besides, this process is confined to the reproduction of ha1f-tone or line (discontinuous tone) images. Finally, the pigment incorporated to the resin coating generally stops the light beams, thus preventing them from reaching the deeper portions of the coating to harden them.

It is also known that images can be obtained by applying a powder on a coating comprising tacky areas and areas which have been hardened by light exposure. In US. Patent 2,090,450, issued on August 17, 1937, there is used an acetal of an aromatic nitrated aldehyde, Le, a non-polymerized product, to form the light-setting coating. This process has many disadvantages. The coat ing is originally tacky, so that it is difficult to handle it and impossible to carry out contact printing. The sensitivity is very low and the dusting-on operation is delicate. The definition and contrast of the resulting images are very poor. Light-setting is produced by polymerization. Accordingly, it was very interesting to have a process wherein coatings showing no tackiness at room temperature are used and which gives images having a good definition and a high contrast.

It is, therefore, an object of my invention to provide a photographic reproduction process in which dimerizable light-setting resins are used, which permits to obtain pigmented images and does not show any of the aforesaid disadvantages. Another object is to provide a process for reproducing continuous tone as well as discontinuous tone images. Still another object is to provide images obtained by said process and, in particular, images on paper whose gloss is a function of the optical density by reflection. Another object is to provide the products obtained by applying said process and, in particular, enamels on ceramic base. Other objects will become apparent from a consideration of the following description and examples.

According to my invention, a dimerizable light-setting resin coating carried by a support is exposed imagewise and is submitted to a softening treatment, in such a manner that the areas of the coating are all the more softened as they have received a smaller amount of exposure and, while the coating is thus differentially softened, there is applied a pigment which adheres in an amount which is the greater as the areas have been more softened, that is less exposed, to finally obtain a reproduction of the original image.

Thus, in the process of my invention, the latent image is developed by adding a pigment without removing any portion of the resin coating; the wash-off operation is therefore eliminated.

It was not obvious that a polymeric system whose physical properties are modified by light might be used for obtaining pigmented images. In fact, tests have shown for instance that o-nitrobenzaldehyde polyvinyl acetal which permits to prepare a photographic resist by a washoff operation after a very short exposure time (1 minute) permits to obtain images having a differential adhesiveness only after exposure times of at least one hour, the resulting images being hardly visible. It is also impossible to obtain an image of a sufficient quality by the process of the invention with a light-sensitive coating comprised of an azide sensitized cyclised rubber which, however, also gives photographic resists by a wash-off operation. Therefore, it is most surprising to find that, by the process of my invention, dimerizable light-setting resins give powder images showing a definition worthy to be compared to that of the images obtained with the usual silver halide emulsions, whereas such products as o-nitrobenzaldehyde polyvinyl acetal, which are light set by isomerization, do not give such images or give hardly visible images.

The differential softening of the resin after exposure may be obtained, for instance, by heating or treating the resin layer with an organic liquid which softens the resin but does not dissolve it. One of these methods will be selected depending on the type of light-sensitive resin used, the former giving better results with certain types of resin, the latter with other types of resin.

Most dimerizable light-setting polymers are comprised of more or less branched linear macromolecules which, either alone or in the presence of photosensitizers, are transformed by the action of light into tridimensional lattices by cross-linking. Such a transformation is accompanied by a reduction of the solubility and of the fusibility. Now, if solubility in a given solvent disappears rather markedly when the exposure received has reached a certain amount, which property has been utilized in the prior processes, penetrability by an organic liquid having an insufiicient solving power is a property which is reduced proportionally to the amount of exposure. The same holds true for the degree of softening obtained by heating a given heat fusible polymer at a given temperature. When a pigment is applied to a coating of a dimerizable light-setting polymer which has been softened by one of the aforesaid methods, it appears that the various areas of the coating accept the pigment all the less as they have received a greater amount of light exposure.

For practising my invention, all the known dimerizable light-setting resins such as polyvinyl cinnamates, polyesters of diols and cinnamylidene maloni-c acid, glycol polyanthranyl-methylmalonates and the like may be used.

The spectral sensitivity of such resins may be extended towards greater Wavelengths by adding suitable sensitizers such as methyl benzothiazolylidene-dithioacetate, which permits, in particular, to obtain a better tone reproduction when a coating of such a sensitized resin is exposed to a color transparency.

Images can be obtained on many bases and, in particular, on glass, ceramic material, metal, paper, wood, plastic materials such as cellulose derivatives or synthetic resins.

For practising my invention, it is possible, after imagewise exposure, to follow various procedures. A uniform layer of pigment may be deposited on the coating, this being followed by softening, or the softening operation may be carried out first, followed by development with a pigment, or else both operations may be accomplished simultaneously.

The pigment may be applied after exposure on the dimerizable light-setting coating by means of a dispersion of said pigment in a volatile swelling liquid, which ensures the differential softening of the coating. Upon evaporation of the liquid, it appears that the pigment is fixed upon the coating in an amount which is the greater as the light exposure received has been the smaller.

If the resin coating shows or permits to see a white surface and if a dark colored pigment is used, a positive image is obtained with respect to the original image. Conversely, a negative image is obtained if the resin coating shows or permits to see a dark surface and if a white or light colored powder is used as a pigment.

Among the organic liquids capable of being used as softening agents are such liquids as turpentine oil, carbon tetrachloride, methylisobutylketone and the like in the case of a dimerizable light-setting resin made up of tetramethylene polycinnamylidenemalonate.

The nature of the pigment is not critical. Carbon black, animal black, non-organic or organic pigments, metal powders and the like may be used, or enamel colors such as those which are sold in France by Etablissements lHospied & Cie, such as Blue D-ll, Red D70 and Black D-91.

In accordance with an embodiment of my invention, it has been found that the images obtained on paper, in particular, when pigments comprised of crystals having an irregular and angular shape are used, show characteristics that had never been obtained up to now. That is, these images are characterized by a gloss or specular reflection ratio which is a function of the optical density by reflection in each point of the image, which gives them an unusual aspect likely to be variously used in the systems in which images are viewed under reflected light. In fact, contrast varies according to the angle of incidence, the reflective power of the black areas being substantially independent of such angle, whereas the reflective power of the highlight areas varies very much with such angle. The images thus defined are a part of my invention. A procedure for obtaining such images is described in Example V.

The process in accordance with my invention is capable of many applications in decorating techniques and, in particular, for preparing enamels on glass, ceramic or metal bases. For instance, an image is developed on a ceramic base with a pigment capable of being glazed and, by firing it at a sufficiently high temperature, the enamel constituted by the pigment is glazed and hardened while the light-sensitive coating is eliminated. An image that does not deteriorate is thus finally obtained.

This process may also be used in letterpress for obtaining reversed negatives or for evaluating a set of color selection negatives. In the latter case, it suffices to prepare three or four pigmented images on a dimerizable light-setting coating applied on a very thin transparent support such as a support of poly (ethylene glycol terephthalate) having a thickness of 35 microns, by exposure through each of the color separation positives, followed by the above described softening and pigmenting operations, using the pigments of the inks that will be used for the printing operation. The correct registering of such images placed on a white paper background will give, prior to the preparation of the letterpress chases, an idea of the printed image that may be obtained.

The process in accordance wit-h my invention may also be used in the processes that resort to differences in wet-tability between the various portions of a surface, such as in lithography. Such differences in wettability may be created by using, for the coating of dimerizable light-setting resin, a hydrophobic resin such as butanediol polycinnamylidenemalonate and by depositing a hydrophilic pigment such as silica, baryta, after imagewise exposure, before, during or after the differential softening treatment.

This process also permits to obtain in a similar manner photographic reproductions on paper or on a transparent film, which have the advantage of being indifferent to the variations of humidity conditions and unaffected by fungi.

The following examples will serve to illustrate more fully the operation of my invention.

Example I.--Ph0l0grapl1y on paper A layer of polytetramethylene cinnamylidene malonate such as described in Michiels et al. US. Patent 2,956,- 878, issued October 18, 1960, sensitized with 3% based on the polyester, of methyl benzothiazolylidene dithioacetate, was coated from a 7.5% SOlutiOn in trichloroethylene on a sheet of baryta paper of the type used in the making of photographic paper, the resulting layer obtained upon drying having a thickness of about 4 to 5 microns. This coating was exposed for four minutes at about 35 cm. from a w. Mazda mercury vapor lamp, through a continuous tone positive silver photographic image on a cellulose triacetate film. After exposure, the paper was placed on a heating plate at a temperature of C. The resin layer being external, it was slightly swabbed with carbon black until the desired density was obtained. A positive black image on a yellow background was obtained, the yellow coloration being caused by the residual sensitizer. This yellow coloration could be removed by washing in acetone after reexposure in full light.

Example II.--P/t0t0graphy on ceramic material A coating of polytetramethylene cinnamylidene malonate was applied, as in the foregoing example, on the white flat enameled surf-ace of an earthenware tile.

An imagewise exposure was made in the same manner, then the earthware tile was placed in an oven at a temperature of C. for ten minutes. Upon being removed from the oven, it was immediately swabbed with black ceramic powder sold by Etablissements lHospied & Cie under the trade name Black D9l. After cooling, the excess of powder was brushed off and the tile was then placed in a ceramists furnace Where the temperature was raised to 960 C. At such a temperature, the lightsensitive polymeric coating was completely charred and the enamel was glazed. Upon cooling, a ceramic reproduction of the original image was obtained whose halftones were remarkably respected.

By repeating three times the coating, exposure (respectively with three separation positives) and dusting-on operations with enamels compatible with one another and giving colors which were similar to the basic colors (cyan, magenta and yellow), a color reproduction on a ceramic base was obtained after a glazing operation.

By purposely depositing powders of different colors on different portions of the image, a decorative effect similar to that of colored photographs was obtained.

V Extlmple III.Pht0graphy 0n ceramic material A solution of polyvinyl cinnamate was coated on the enameled surface of an earthenware tile and the coating was exposed imagewise for eight minutes, under the conditions of the foregoing example. A dispersion of Black D-91 in turpentine oil prepared in a ball mill was then spread over all the coated surface. After air drying, the tile was placed in an oven at 200 C. for a few minutes. The excess of pigment was removed with a dry brush, then by washing in alcohol. The enamel was fired as in Example II.

Example I V.-Ph0t0graplty on ceramic material An earthenware tile was used, as in Examples II and III, on the surface of which was coated a toluene solution of polyhexamethylene anthranylmethylmal onate. This polyester was obtained by the polycondensation of hexanediol-l,6 and ethyl anthranylmethylmalonate, the latter being obtained by reacting chloromethyl-9-anthracene with the monosodic salt of ethyl malonate. The coating was exposed imagewise as in the foregoing examples, heated at 200 C. and treated as in Example II. A good quality black-and-white photograph on a ceramic base was obtained.

Example V.-Ph0t0grapl1y on paper Example VI.-Preparati0n of a reversed internegative for copying on a letterpress plate A negative halftone photographic plate was prepared in a usual manner. This plate could not be used as such for copying on a metal plate. It was necessary to reverse the image, which is usually accomplished by stripping the gelatin pigmented with silver grains from its support and applying it on its other side.

In accordance with my invention and in order to avoid this stripping operation, a lightsensitive film was prepared by uniformly coating tetramethylene polycinnamylidene malonate sensitized with methyl benzothiazolylidenedithioacetate on a polyethyleneglycol terephthalate film having a thickness of 35 microns. After drying, the film was pressed in contact with the previously obtained halftone negative, the lightsensitive polymer being in contact with the gelatin and it was exposed through said negative for two minutes at 35 cm. from a 125 w. Mazada mercury vapor lamp. The film was taken from the halftone negative and placed on a metal plate heated at 100 C., the sensitive surface being outside, carbon black was swabbed thereon and the resulting negative which was the reversed image of the original one was thoroughly brushed. It was rapidly washed in acetone in order to remove the residual sensitizer, after reexposure for a few minutes in full light. This negative which was the reversed image of the original one could be used as such for copying on metal for the purpose of obtaining afterwards a process block for letterress use.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A photographic continuous tone image reproduction process comprising exposing to a light image a coating of polyetetramethylene cinnamylidenemalonate sensitized by methyl benzothiazolyidene-dithioacetate, applied to a support, so as to set said resin imagewise by cross-linking, heating said coating at a temperature of from to 240 C. in order to soften its areas in inverse ratio to the amount of light exposure and, while said coating is thus differentially softened, applying a pigment which adheres to the coating in an amount which is the greater as the areas have been more softened, i.e. have received a smaller amount of light exposure, to finally obtain a continuous tone reproduction of the original image.

2. A photographic continuous tone image reproduction process comprising exposing to a light image a coating of a cross-linkable light-setting polymeric resin applied to a ceramic base, so as to set said resin imagewise by cross-linking, heating said coating at a temperature between the melting point and the charring point of said resin in order to soften its areas in inverse ratio to the amount of light exposure and, while said coating is thus differentially softened, applying a pigment capable of being glazed which adheres to the coating in an amount which is the greater as the areas have been more softened, i.e. have received a smaller amount of light exposure, to obtain a continuous tone image reproduction of the original image, and firing the ceramic base at the glazing temperature to convert the pigment into enamel and simultaneously decompose the resin.

3. A photographic continuous tone image reproduction process comprising exposing to a light image a coating of polytetramethylene cinnamylidenemalonate sensitized by methyl benzothiazolylidene-dithioacetate, applied to a ceramic base, so as to set said resin imagewise by cross-linking, heating said coating at a temperature of from 80 to 240 C. in order to soften its areas in inverse ratio to the amount of light exposure and, while said coating is thus differentially softened, applying a pigment capable of being glazed which adheres to the coating in an amount which is the greater as the areas have been more softened, i.e. have received a smaller amount of light exposure, to obtain a continuous tone reproduction of the original image, and firing the ceramic base at the glazing temperature to convert the pigment into enamel and simultaneously decompose the resin.

4. A photographic continuous tone image reproduction process comprising exposing to a light image a coating of polyvinyl cinnamate applied to a support, so as to set said resin imagewise by cross-linking, applying on said coating a dispersion of a pigment in turpentine oil in order to soften its areas in inverse ratio to the amount of light exposure and to make the pigment adhere to said coating in an amount which is the greater as the areas have been more softened, i.e. have received a smaller amount of light exposure and removing the excess of dis persion to finally obtain a continuous tone image reproduction of the original image.

5. A photographic continuous tone image reproduction process comprising exposing to a light image a coat ing of polytetramethylene cinnamylidenemalonate applied to a support, so as to set said resin imagewise by crosslinking, applying on said coating a dispersion of a pigment in turpentine oil in order to soften its areas in inverse ratio to the amount of light exposure and to make the pigment adhere to said coating in an amount which is the greater as the areas have been more softened, i.e. have received a smaller amount of light exposure, and removing the excess of dispersion to finally obtain a continuous tone reproduction of the original image.

6. A photographic continuous tone image reproduction process comprising the steps:

(1) exposing to an original light image, a coating of a polymeric resin that undergoes cross-linking on light exposure, said resin being selected from the class consisting of polytetramethylene cinnamylidenemalonate, polyvinyl cinnamate and polyhexamethylene anthranylmcthylmalonate applied to a support, so as to set the said resin imagewise by cross-linking;

(2) softening said coating in inverse proportion to the amount of light exposure; and

(3) contacting said differentially softened coating with a powder which adheres to said coating in an amount which is directly proportional to the amount of softening to produce a continuous tone image reproduction of the said original image.

7. A photographic continuous tone image reproduction process of claim 6 in which the light image exposed resin layer is softened in inverse proportion to the amount of light exposure by heating the said layer to a temperature between the softening point and the charring point of said resin layer.

8. A photographic continuous tone image reproduction process of claim 6 in which the light image exposed resin layer is softened in inverse proportion to the amount of light exposure by contacting the said layer with an organic solvent which softens but does not dissolve said resin layer.

9. A photographic continuous tone image reproduction process of claim 6 in which the support of the resin coating is paper.

10. A photographic continuous tone image reproduction process comprising the steps:

(1) exposing to an original light image, a coating of a polymeric resin that undergoes cross-linking on light exposure, said resin being selected from the class consisting of polytetramethylene cinnamylidenemalonate, polyvinyl cinnamate, and polyhexamethylene anthranylmethylmalonate applied to a support, so as to set the said resin imagewise by cross-linking;

(2) contacting said image exposed coating with a dispersion of a powder in a resin softening liquid selected from the class consisting of turpentine oil, carbon tetrachloride, and methyliso'butylketone, said powder adhering to said coating in an amount which is directly proportional to the amount of softening to produce a continuous tone image reproduction of the said original light image.

References Cited by the Examiner UNITED STATES PATENTS 52,503 2/1866 Obernetter 9634 416,015 11/1889 Smalz 96-34 2,090,450 8/1937 Kogel 961 15 2,732,297 1/1956 Minsk et al 9634 2,956,878 10/1960 Michiels et al 9611S 3,052,539 9/1962 Greig 961 3,060,023 10/1962 Burg et al 96115 3,066,023 11/ 1962 Schlesinger 961 3,079,253 2/1963 Greig 961 FOREIGN PATENTS 3,445 3/1885 Great Britain.

NORMAN G. TORCHIN, Primary Examiner. 

2. A PHOTOGRAPH CONTINUOUS TONE IMAGE REPRODUCTION PROCESS COMPRISING EXPOSING TO A LIGHT IMAGE A COATING OF A CROSS-LINKABLE LIGHT-SETTING POLYMERIC RESIN APPLIED TO A CERAMIC BASE, SO AS TO SET RESIN IMAGEWISE BY CROSS-LINKING SAID COATING AT A TEMPERATURE BETWEEN THE MELTING POINT AND THE CHARRING POINT OF SAID RESIN IN ORDER TO SOFTEN ITS AREAS IN INVERSE RATIO TO THE AMOUNT OF LIGHT EXPOSURE AND, WHILE SAID COATING IS THUS DIFFERENTIALLY SOFTENED, APPLYING A PIGMENT CAPABLE OF BEING GLAZED WHICH ADHERES TO THE COATING IN AN AMOUNT WHICH IS THE GREATER AS THE AREAS HAVE BEEN MORE SOFTENED, I.E. HAVE RECEIVED A SMALLER OF LIGHT EXPOSURE, TO OBTAIN A CONTINUOUS TONE IMAGE REPRODUCTION OF THE ORIGINAL IMAGE, AND FIRING THE CERAMIC BASE AT THE GLAZING TEMPERATURE TO CONVERT THE PIGMENT INTO ENAMEL AND SIMULTANEOUSLY DECOMPOSE THE RESIN. 